The present invention relates to a chip carrier film in which an insulating film provided on a surface of a base film has a different coefficient of curing shrinkage from that of an insulating film provided on the back of the film and a method of manufacturing the chip carrier film, and a liquid crystal display using the chip carrier film.
There has widely been used a TCP (Tape Carrier Package) mount method of connecting a liquid crystal display panel and a circuit board through a film mounting thereon a driver IC (for example, Japanese Unexamined Patent Publication No. 169793/1995). Based on the Japanese Unexamined Patent Publication No. 169793/1995, the structure of the TCP will be summarized. FIG. 5 is a plan view showing the TCP and FIG. 6 is an enlarged sectional view taken along the line A—A in FIG. 5. In a device hole 21 provided on a base film 20 formed of polyimide, a driver IC 22 is connected through a bump to a circuit pattern (a copper foil plated with tin) 23 provided on the film 20. The circuit pattern 23 is formed on the base film 20 through an adhesive layer 24 and the surface of the circuit pattern 23 is covered with a solder resist 25 and is thus protected. Moreover, a high reliability resin (sealing material) 26 and a reinforcing resin 27 are provided around the driver IC 22. The circuit pattern 23 has connecting terminal pads 28 and 29 and inner leads 30 and 31 connected thereto.
However, the TCP has the following problems.
(1) Fine pitch (corresponding to a 40 μm pitch)
With an increase in fineness of the liquid crystal display panel, an advanced mounting technique for implementing a fine pitch corresponding to a 40 μm pitch has been desired. The fine pitch of a copper wiring formed on the film is closely related to a thickness thereof. More specifically, it has been supposed that the thickness (17 to 35 μm) of a conventional copper wiring is to be reduced to approximately 10 μm. However, if the thickness of the copper wiring is reduced, there is another problem that the copper wiring of a bump connecting portion B in FIG. 6 is bent. Thus, it has been supposed that a very fine pitch is hard to implement through the TCP mount method.
(2) Reduction in manufacturing cost
By the request of a reduction in a frame of the liquid crystal display, a film having a chip mounted thereon is accommodated in the liquid crystal display with the film being bent. Because of the limitations of a manufacturing process of the TCP chip, however, it is hard to reduce the thickness (approximately 70 μm) of the film to be used. Therefore, the bent portion of the film should be subjected to a special processing, resulting in an increase in the manufacturing cost. More specifically, it is necessary to carry out the step of coating the bent portion with a reinforcing resin after providing a slit in the bent portion.
In order to achieve the above-mentioned problems, attention has been paid to a COF (chip on film) mount method for eliminating a device hole of a film and mounting a driver IC on the film in place of the TCP mount method. In the COF, it has been supposed that the thickness of a base film can also be reduced (35 to 40 μm).
FIG. 7 is a sectional view showing a conventional COF in which the driver IC is mounted thereon. A circuit pattern 23 (a copper foil surface plated with tin) to be electrically connected to the driver IC 22 is formed on the surface of the base film 20 (polyimide) and is insulated and protected through the solder resist 25. The driver IC 22 is connected to the circuit pattern 23 through a bump 32 in a portion of the circuit pattern 23 which does not cover the solder resist 25. A resin 26 is applied as a sealing material in the bump connecting portion. Thus, the COF technique is characterized in that the driver IC 22 is mounted on the base film 20 without using the device hole.
Japanese Unexamined Patent Publication No. 215448/1992 has described the basic concept of the COF mount method in which a semiconductor chip can be directly mounted without providing a device hole on a base film of a chip carrier (see column 7, lines 6 to 11).
In case of using an existing COF, however, it has been found that the following problem arises. The number of the COFs to be connected to a 15 inch liquid crystal display panel is more than 10 and less than 20 and a work for mounting the COF on the liquid crystal display panel is carried out through a high speed automatic device. However, the thickness of the base film is reduced (35 to 40 μm) so that the film is easily bent. Consequently, it has been found that a work for delivering the film is very complicated and the manufacture is hindered considerably.
More specifically, in the case in which the high speed automatic device is to be used, it is necessary to mount one of ends of a base film on a liquid crystal display panel in a state in which the other end of the film is held in an arm of the device. Therefore, the base film having a low rigidity is suspended by the self weight of the driver IC chip. Consequently, a situation in which the mounting on the liquid crystal display panel cannot be carried out well is caused easily.
The present invention has been made to solve the above-mentioned problems and has a first object to provide a chip carrier film capable of preventing a base film from being suspended due to the self weight of a semiconductor chip and of carrying out mounting without a hindrance when holding the base film through a delivery device.
It is a second object of the present invention to provide a chip carrier film capable of preventing the base film from being suspended by the self weight of the semiconductor chip, carrying out the mounting without a hindrance and enhancing the reliability of a terminal connection when holding the base film through a delivery device.
It is a third object of the present invention to provide a method of manufacturing a chip carrier film capable of preventing a base film from being suspended due to the self weight of a semiconductor chip and of carrying out mounting without a hindrance when holding the base film through a delivery device.
It is a fourth object of the present invention to provide a liquid crystal display using a chip carrier film capable of preventing a base film from being suspended due to the self weight of a semiconductor chip and of carrying out mounting without a hindrance when holding the base film through a delivery device.
The Japanese Unexamined Patent Publication No. 169793/1995 has disclosed that the problem of the warp of a TCP film base material having an LSI mounted thereon can be solved by coating the back face of a film base material with a resin made of the same material (an epoxy based resin) as a solder resist covering an inner lead (see column 6, paragraph [0028] in the publication, for example). According to the publication, however, the material of the solder resist and that of the back resin are the same epoxy based resins, which is entirely different from the technical concept of the present invention in which the characteristics of films formed on both surfaces of a film are varied based on a difference in a coefficient of curing shrinkage.